chore: centralize deploy/install CD actions in twentyhq/twenty (#19454)

## Summary

- Adds `deploy-twenty-app` and `install-twenty-app` composite actions to
`.github/actions/` so app repos can reference them remotely — same
pattern as `spawn-twenty-app-dev-test` for CI
- Updates `cd.yml` in template, hello-world, and postcard to use
`twentyhq/twenty/.github/actions/deploy-twenty-app@main` /
`install-twenty-app@main` instead of local `./.github/actions/` copies
- Removes the 6 local action files that were duplicated across template
and example apps

**Before** (each app repo carried its own action copies):
```yaml
uses: ./.github/actions/deploy
```

**After** (centralized, like CI):
```yaml
uses: twentyhq/twenty/.github/actions/deploy-twenty-app@main
```


Made with [Cursor](https://cursor.com)

packages/create-twenty-app/src/constants/template/github/workflows/cd.yml

@@ -30,13 +30,13 @@ jobs:
           ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: Deploy
-        uses: ./.github/actions/deploy
+        uses: twentyhq/twenty/.github/actions/deploy-twenty-app@main
         with:
           api-url: ${{ env.TWENTY_DEPLOY_URL }}
           api-key: ${{ secrets.TWENTY_DEPLOY_API_KEY }}
 
       - name: Install
-        uses: ./.github/actions/install
+        uses: twentyhq/twenty/.github/actions/install-twenty-app@main
         with:
           api-url: ${{ env.TWENTY_DEPLOY_URL }}
           api-key: ${{ secrets.TWENTY_DEPLOY_API_KEY }}